What are the risk factors for malignant mesothelioma?
There are several risk factors that increase the likelihood that a person will develop mesothelioma. The primary risk factor is asbestos exposure. Exposure to this very harmful substance can significantly enhance the chances of contracting the disease. Other secondary factors include exposure to radiation, zeolite, simian virus 40 (SV40) and tobacco. We discuss each of these risk factors in more detail below.
Exposure to asbestos is the leading risk factor associated with mesothelioma. Asbestos is an insulating material comprised of magnesium-silicate mineral fibers. It was favored by builders and contractors for many years for its low heat conductivity and resistance to melting and burning. Since researchers have identified more and more links between mesothelioma and exposure to asbestos, the material is now less widely used. Prior to this discovery, however, millions of Americans have experienced serious exposure to this harmful substance.
Over 700,000 schools and buildings in the United States today contain asbestos insulation as reported by the US Environmental Protection Agency. Asbestos exposure doesn’t stop there, however. Asbestos is often found in ship yards, manufacturing facilities, railway facilities and construction sites. Blue collar workers are at the highest risk for developing mesothelioma due to occupational exposure and include those who work in mines, factories, shipyards, construction sites, railroads and for insulation manufacturers and gas mask manufacturers. The occupations most widely affected are miners, factory workers, railroad workers, ship builders and construction workers - especially those who install asbestos containing insulation. Sometimes family members related to the workers receive second hand exposure to asbestos from the dust and fibers that were brought home on the workers clothes and also become at risk for contracting mesothelioma.
Serpentine fibers and amphiboles are the 2 primary types of asbestos used. Chrysotile is a form of serpentine fiber and the most frequently used. These fibers tend to be curly and flexible. Amphibole fibers, however, are generally straight and thin and usually comprise one of five types: crocidolite, amosite, anthrophylite, tremolite, and actinolyte. The crocidolite type of Amphiboles is thought to be the leading contributor to cancer caused by asbestos. Serpentine fibers are dangerous as well, however, and have also been linked to mesothelioma.
Some research points to the fact that inhaled asbestos fibers cause a physical irritation resulting in cancer rather than the cancer being caused by a reaction that is more chemical in nature. As fibers are inhaled through the mouth and nose they are cleared from the body by adhering to mucus in the nose, throat and airways and then get expelled by coughing or swallowing. The Amphibole fibers (long and thin) do not clear as easily and it is therefore thought that they can embed into the lining of the lungs and chest and result in mesothelioma.
Asbestosis (scar tissue in the lungs) or lung cancer can also be caused by the inhalation of asbestos fibers. In fact, people exposed to asbestos are seven times more likely to develop lung cancer over the general public. Workers who sustain high levels of asbestos exposure are more likely to die from asbestosis, lung cancer or mesothelioma than any other disease. It is also believed that the action of coughing up and swallowing asbestos could contribute to a form of mesothelioma originating in the abdomen called peritoneal mesothelioma. Mesothelioma has been found to exist in other organs of the body as well such as the larynx, pancreas and colon, but those instances are extremely limited compared to lung cancer incidents.
The chance of developing mesothelioma is in direct proportion to the duration and amount of asbestos exposure that an individual sustains. Those who are exposed to high levels of asbestos at a young age, for long periods of time have a greater risk of being diagnosed with mesothelioma than those who have short, low level exposure. Another important consideration is that Mesothelioma can take a long time to manifest. Often, twenty to forty years can elapse from the time of exposure to diagnosis. Genetic factors can also play a role which explains why not everyone exposed to asbestos develops and asbestos related disease.
Thorium dioxide (Thorotrast), a substance used in x-ray tests in the past has reported links to pleural mesothelioma and peritoneal mesothelioma. The use of Thorotrast has been discontinued for many years due to this discovery.
Some mesothelioma cases in the Anatoli region within Turkey have been linked to Zeolite, a silica based mineral with chemical properties similar to asbestos found in the soil there.
Simian Virus 40 (SV40)
Some scientists have found the simian virus 40 (SV30) in mesothelioma cells from humans and have been able to create mesothelioma in animals with the virus. The relationship between this virus and mesothelioma is still unclear, however, and further research is being conducted to gain clarity on this potential link.
Smoking alone is not linked to mesothelioma, but smokers who are exposed to asbestos have a much higher chance of developing lung cancer (as much as fifty to ninety percent higher). Research indicates that lung cancer is the leading cause of death among asbestos workers.